1. Skeletal System

2. Endochondral Ossification
“inside cartilage”
Form within hyaline cartilage
Cartilage framework for organized ossification
~ 6 wks thru ~ 25 yrs
Growth pattern of long bones

3. Fetal Bone Development

4. Infant to ~25 yrs Long Bone –Epiphyseal Plate

5. Endochondral Ossification

7. Endochondral Ossification
Mesenchymal model forms during development
Mesenchymal differentiate into chondroblasts at center of growing cartilage
Chondroblasts grow (hypertrophy) enlarged lacunae create reduce matrix to thin struts that calcify
Vascularization of cartilage
Perichondrium cells convert to osteoblasts
Blood vessels penetrate cartilage bringing blood supply & osteoblasts
Oteoblasts produce spongy bone
Remodelling of spongy bone to compact bone

8. Mesenchyme Cells form Bone Model

9. Mesenchyme Cells Differentiate to Chondroblasts
Chondroblasts Convert tissue to Cartilage

10. Perichondrium Develops Around Cartilage Model

11. Cartilage Grows in Length & Girth
Length Growth is
Called interstitial growth
Width Growth is
Called appositional growth

12. Proliferation vs Hypertrophy
Edges
Center

13. Endochondral Ossification
Cartilage framework initial step
As cartilage grows (proliferation), centrally located chondrocytes grow (hypertrophy) and rupture
Begins ossification of cartilage
At margins cartilage model continues to grow

14. Cartilage Continues to Grow

15. Hypertrophied Cells Burst Stimulating Calcification of Matrix

16. Hypertrophied Cells Burst Stimulating Calcification of Matrix

17. Osteoblast Produce Bone Collar
Vascularization Stimulates Mesenchymal Cells to Convert to Osteoblasts
Osteoblast Produce Bone Collar

18. Perichondrium Converts to Periosteum

19. Vascularization of Tissue Carries Osteoblast into Matrix Forming Primary Ossification Center

20. Primary Ossification Center

21. Primary Ossification Center Continues to Grow at Edges
Ossification begins in diaphysis & migrates toward the epiphysis

22. Cartilage Continues to Grow & Ossification Continues towards ends of Diaphysis

23. Cartilage Continues Proliferation & Hypertophy

24. Ossification of Cartilage Continues Towards ends of shaft
Center

25. Calcified Cartilage Matrix

26. Forms Spongy Bone

27. Form Trabeculae of Spongy Bone

28. Osteoclast Remodel Spongy Bone to Compact

29. Bone Remodeling

30. Bone Remodeling Forms Medullary Cavity

31. Forms Haversian System

32. Endochondral Ossification
Blood vessels & osteoblasts migrate into epiphysis
Secondary ossification centers
Bone ossification remains incomplete
Epiphyseal plate
Site of continued bone growth
Produces VERY structured compact bone

33. Blood Vessels Enter into Diaphysis

34. Secondary Ossification Centers Form
Ossification of epiphysis

35. Secondary Ossification Centers

36. Cartilage at Edges Persists as Articular Cartilage

37. Metaphysis Location of epiphyseal plate Site of bone elongation
Growing cartilage plate persists
Zone of proliferation
Zone of Hypertrophy

38. Epiphyseal Plate

39. Long Bone Elongation

40. Bone Elongation Chondrocytes divide and produce new cartilage
Diaphysis- chondrocytes replaced by invading osteoblasts
During growth stage chondrocyte activity matches osteocyte activity
At maturation osteocyte invasion is FASTER than chondrocyte division
Puberty- Sex hormones stimulate osteoblast & chondrocyte activity aka growth “spurt”

41. Chondrocyte Proliferation

42. Osteocyte Invasion

45. Bone Growth Disorders Achondroplastic dwarf
Results from slow epiphyseal plate growth & early plate closure
Chondrocytes have slower activity
Results in normal trunk growth & stunted long bone growth

47. Bone Growth Disorders Marfan’s syndrome
Dominant genetic disorder
Abnormal connective tissue growth
Hyperactive chondrocytes & epiphyseal plate
Symptoms- long thin limbs